1. Field of the Invention
The present invention relates to a thermal transfer printing method and an image-forming layer transfer medium using a printing means such as a thermal head, an optical head like a laser, and electrical head, and more particularly to a thermal transfer printing method and an image-forming layer transfer medium capable of obtaining an excellent printing image on any type of image-receiving medium such as a plain paper in a sublimation type thermal transfer printing.
2. Description of the Prior Art
In the thermal transfer printing of sublimation type, there is known a method of forming a dyeing layer first on an intermediate medium, then printing a thermal transfer image into the dyeing layer on the intermediate medium, and subsequently transferring thus printed dyeing layer onto an image-receiving medium such as a plain paper, thereby finally forming an image on the image-receiving medium. (For example, Unexamined Japanese Patent Application No. HEI 4-141486)
In such a conventional printing method, a problem will arise when, after the image is once printed on the intermediate medium, the printed dyeing layer is transferred from the intermediate medium to the image-receiving medium. More specifically, the dyeing layer is subjected to application of heat when the image is printed into the dyeing layer and/or when the dyeing layer is transferred to a plain paper. If the printing density of the dyeing layer is too high, a part of dyestuff possibly penetrates the dyeing layer and possibly contaminates the intermediate medium. Since the intermediate medium is repeatedly used, the next dyeing layer is newly formed on the intermediate layer to print the image in this dyeing layer and then transfer the image onto the image-receiving medium in the same manner as the previous printing operation. Thus, there is a possibility that the previously printed image remaining on the intermediate medium may be unwantedly transferred onto the newly formed dyeing layer, thus causing a problem that the old print image contaminates the new print image formed in the new dyeing layer.
Furthermore, penetration of dyestuff through the dyeing layer will cause another problem such that the print density obtained is lower than expected. This is because a part of dyestuff penetrates the dyeing layer so deep that it dyes the intermediate medium, for example, in a case where the dyestuff to be completely maintained in the dyeing layer during a printing operation partly includes a higher print density region, or in a case where numerous colors are simultaneously printed.
Moreover, another problem will arise when a material having low glass transition point (or softening point) is adopted as a dyeing layer in order to gain excellent printing sensitivity. Because, the dyeing layer on a support may be thermally melted onto the reverse surface of the support when the transfer medium including the dyeing layer is maintained in a wound condition at a higher temperature.
Meanwhile, maintaining the dyeing layer at a lower temperature is normally required when the dyeing layer is transferred from the transfer medium to the intermediate medium, or when the dyeing layer is transferred from the intermediate layer to the image-receiving medium such as a plain paper.